The invention relates to tires for highway vehicles of the heavy-vehicle type, and in particular to those tires which are provided with a device for deflecting the lateral sprays of water when a vehicle fitted with said tires travels over a water-covered road surface.
When traveling during rainy weather, the maneuvers of overtaking and passing with a heavy vehicle are frequently very tricky, taking into account the large quantities of water which are sprayed sideways by said vehicle and which, when they reach the windshields of passenger vehicles, considerably reduce the visibility. It has been known for a long time, for example from U.S. Pat. No. 3,204,681, to provide the sidewalls of aircraft tires with projecting elements extending in the circumferential direction over the outer surface of said tires. These elements form protuberances, the role of which is to deflect the trajectory of the flow of sprayed liquid in order to prevent this flow from being sprayed too high towards the engines.
A tire for a heavy vehicle is generally composed of two beads intended to be in contact with a mounting rim, a crown provided with a tread having a running surface which is intended to come into contact with the ground during travel, and two sidewalls which provide the connection between this tread and the beads.
Such a tire is reinforced by a carcass reinforcement extending from one bead to the other and a reinforcement armature for the crown which is located radially to the outside of the carcass reinforcement, this crown reinforcement comprising at least two stacked plies of reinforcements, that is to say, plies which are placed one on the other. Each ply of the crown reinforcement is generally composed of a plurality of reinforcements arranged so as to form an angle from 0xc2x0 to 70xc2x0 with the circumferential direction, but it is not however ruled out that the angle of the reinforcements may be greater than 70xc2x0.
The tread of a heavy-vehicle tire is provided with a tread pattern formed of elements in relief defined by cutouts (grooves and/or incisions) intended to provide the tire, among other things, with adhesion performance on wet roads.
The tire occupies a space of maximum width L measured at the level of its sidewalls when it is mounted on its mounting wheel and is subjected to its rated conditions of use in terms of pressure and load (L represents the maximum distance between the points of the sidewalls which are axially farthest apart).
It has been observed that by following the conventional rules of adding a protuberance to one of the sidewalls of this tire associated with the hysteretic nature of the rubber mixes forming the tread and the crown, heating of said mixes occurred in the vicinity of the ends of the reinforcement plies of the crown. In particular, the rubber mix serving as a decoupling means between the ends of the working plies works at high temperatures, resulting in a change in the characteristics of said mix and in separation or rupture in this decoupling mix.
The aim of the tire according to the invention is to achieve good deflection of the flow of liquid sprayed laterally during travel on water-covered ground without causing an increase in the operating temperature of the tire in the tread and in particular in the vicinity of the ends of the reinforcement plies of the crown.
With this aim, the heavy-vehicle tire according to the invention comprises:
two beads intended to be in contact with a mounting rim,
a crown provided with a tread having a running surface intended to come into contact with the ground during travel,
two sidewalls providing the connection between this tread and the beads,
a carcass reinforcement extending from one bead to the other,
a reinforcement armature for the crown, located radially to the outside of the carcass reinforcement, this crown reinforcement comprising at least two superposed plies, each ply being provided with reinforcements in the form of cords or cables,
a protuberance projecting from at least one of the sidewalls, this protuberance being limited by an upper wall located radially to the outside and a lower wall located radially to the inside, the intersection of said walls occurring along a line joining the points C of this protuberance, on respective sectional planes of the tire, which are located axially farthest to the outside of said protuberance, the angle xcex1, measured in a plane containing the axis of the tire, between the axial direction and a straight line tangent both to the edge of the tread and to the protuberance being less than 45xc2x0.
Viewed in meridian section, the tire according to the invention is characterized in that:
the point of intersection C of the profiles of the upper and lower walls of the protuberance is located at a distance from the equatorial plane XX which is at most equal to half the distance L between the points M of the sidewalls which are axially farthest when the tire is subjected to its rated conditions of pressure and of load, and the distance of the point C from the axis of rotation is strictly greater than the distance of said points M relative to the same axis,
the upper profile of the protuberance extends from the point C and joins the sidewall profile at a point K, said point being defined as the intersection of the outer profile of the tire with the extension of the average profile of the last ply of the crown reinforcement,
the angle xcex4 between a first straight line D1 and a second straight line D2 is greater than or equal to 60xc2x0, the first straight line D1 being defined as the straight line passing through the point K and tangent to the upper profile of the protuberance and the second straight line D2 being defined as the straight line passing through the point K and tangent to the profile of the sidewall which extends radially to the outside the upper profile of the protuberance from said point K.
xe2x80x9cSidewall profilexe2x80x9d is understood to mean the profile comprising the following three parts of a profile:
part of the sidewall profile joined to one of the beads,
part of the sidewall profile joined to the running surface of the tread,
outer profile of the protuberance located between the preceding two profiles.
Surprisingly, it has in fact been observed that the position of the connection of the upper surface of the protuberance with the profile of the sidewall close to the running surface has a major effect on the heating above and in the vicinity of the ends of the reinforcement plies of the crown which results from the stresses withstood by a heavy-vehicle tire subjected to rated conditions of use.
The proposed solution makes it possible to optimize both the efficiency with regard to the lateral spraying of water and the endurance of the crown of the tire.
Preferably, and in order not to make the tire too heavy, only the sidewall intended to be mounted on the outer side of the vehicle is provided with a protuberance according to the invention.
Preferably, to obtain effective deflection of the lateral sprays, the angle xcex1 of the protuberance lies between 32xc2x0 and 37xc2x0.
In the majority of cases, a heavy-vehicle tire is provided with a tread which itself is provided with a tread pattern composed of a plurality of cutouts, the depth of which is defined according to the desired performance, and in particular according to the acceptable wear limit of said tread. In order to prevent a protrusion fitted on a tire sidewall from rubbing against the ground during the travel of said tire and very substantially reducing the effectiveness of said protuberance in laterally deflecting the flow of liquid, it is advisable to provide for the distance between the running surface of the tire subjected to its rated conditions of use and the point of the upper profile of each protuberance which is located radially farthest to the outside to be at least equal to the permitted maximum depth of wear of the tread.
The effectiveness of the solution proposed is all the greater, the more the part of the tread located in the vicinity of the end of the working plies has the ability to dissipate the heat produced in this region during travel of the tire. For effective dissipation of the heat produced in the tire during travel, it is advantageous to provide for the upper profile of the protuberance, starting from the point of connection K with the sidewall profile, to be formed by a first curved part extending said sidewall profile radially towards the inside starting from said point K, such that said profile of the protuberance is, at least in part, located radially to the inside of the extension of the average profile of the final crown ply.
The average direction of the sidewall profile radially to the outside of said point of connection K corresponds to a direction tangent to the sidewall and passing through the same point K.